Research interests in our group

The group has currently three main research directions:

  • Nanoscale thermal transport, especially focusing on phononic crystals and near-field transport
  • Development of superconducting materials and devices, especially ultrasensitive superconducting radiation detectors and their applications from sub-mm to X-ray energies
  • Utilizing novel nanofabrication and imaging techniques for interdisciplinary projects, such as nanoscale biological imaging with helium ion microscope (HIM) 

 

Selected publications

Engineering thermal conductance using a two-dimensional phononic crystal
Nobuyuki Zen, Tuomas A. Puurtinen, Tero J. Isotalo, Saumyadip Chaudhuri, and Ilari J. Maasilta
Nature Communications 5, 3435 (2014)

Here we show for the first time that phonon thermal conductance can be strongly modified coherently, by orders of magnitude,  using two-dimensional hole array phononic crystals. Calculations performed using finite element method agreed with the experiment and demonstrated that the effect arises from strong reduction of the group velocities of the modified phonon modes.  

Broadband Ultrahigh-Resolution Spectroscopy of Particle-Induced X Rays: Extending the Limits of Nondestructive Analysis
M. R. J. Palosaari, M. Käyhkö, K. M. Kinnunen, M. Laitinen, J. Julin, J. Malm, T. Sajavaara, W. B. Doriese, J. Fowler, C. Reintsema, D. Swetz, D. Schmidt, J. N. Ullom, and I. J. Maasilta
Phys. Rev. Applied 6, 024002 (2016)

PIXE spectroscopy is a widely used accelerator-based method for elemental analysis, down to trace level impurities. This work, performed in collaboration with the JyU Accelerator laboratory and NIST Boulder, demonstrates for the first time that practical PIXE spectroscopy can be performed with a cryogenic X-ray transition-edge sensors array, with over an order of magnitude improved energy resolution to previous state-of-the-art.  We show that the technique offers great promise in the elemental analysis of thin-film and bulk samples, especially in the difficult cases where tens of different elements with nearly overlapping emission lines have to be identified down to trace concentrations. In the demonstrated cases, standard silicon drift detectors could not resolve all elements.  

Imaging Bacterial Colonies and Phage–Bacterium Interaction at Sub-Nanometer Resolution Using Helium-Ion Microscopy
Miika Leppänen, Lotta-Riina Sundberg, Elina Laanto, Gabriel Magno de Freitas Almeida, Petri Papponen and Ilari J. Maasilta
Advanced Biosystems 1, 1700070 (2017)

This paper, in collaboration with the biology department, demonstrates the first helium ion microscope (HIM) imaging of bacterial colonies interacting with viruses of bacteria, or bacteriophages. Furthermore, by controlling the He beam dose or by using heavier Ne ions, we milled out material in the samples, allowing for subsurface imaging and in situ sectioning. HIM seems to offer great opportunities to advance the studies of microbial imaging.